This is a National Phase of International Application No. PCT/GB2003/003948, filed on Sep. 11, 2003, which claims priority from Great Britain Patent Application No. 0224646.0, filed on Oct. 23, 2002.
The present invention relates to a continuously variable ratio transmission unit (“variator”) and to a method of assembly thereof.
The general construction of variators of toroidal-race, rolling-traction type will be familiar to the skilled person. Typically two toroidal cavities are defined between facing surfaces of a set of variator discs all of which are mounted for rotation about a common axis. Drive is transmitted between the discs by a set of rollers in both of the cavities and the inclination of the rollers with respect to the discs is able to change in accordance with changes in variator drive ratio. A biasing force, along a direction transverse to the disc axis, is applied to each roller by an actuator which in existing designs is of hydraulic type.
Fabrication and in particular assembly of existing variators is somewhat complex. The discs, actuators and rollers are typically all mounted in a housing and assembling the various parts inside the housing is in current prototypes a somewhat time consuming process not easy to automate or adapt to production line techniques.
A first object of the present invention is to provide a variator which is capable of straightforward assembly.
The need to provide for hydraulic fluid supply to the several actuators has meant some complication in the machining of the variator's components, particularly the housing. The applicant has previously proposed, in order to simplify construction, to form passages for the fluid supply between confronting faces of a multi-part casing—see its published International Patent Application PCT/GB99/02968. Nonetheless an additional or alternative object of certain embodiments of the present invention is to provide, in a variator, a means of fluid supply to the hydraulic actuators which is straightforward in fabrication and assembly.
The shape of the variator housing is in many cases a crucial design issue. The current need is for variators which can be installed in existing motor vehicle designs. Hence in rear wheel drive cars the variator is to be installed in the transmission tunnel. Both excessive length and width of the variator could be problematic, and in particular laterally projecting “lobes” needed in existing designs to accommodate the roller control actuators, create installation difficulties. An additional or alternative object of the present invention is to provide a variator whose external shape is suited to installation in a motor vehicle.